Polymers for the treatment of boiler water

ABSTRACT

A method for controlling the deposition of scale imparting species on the structural surfaces of steam generating systems comprising the use of a water soluble polymer having the structure ##STR1## wherein R 1  is H or lower (C 1  -C 4 ) alkyl, R 2  is (CH 2  --CH 2  --O) n , ##STR2## or a mixture of both, and n is an integer of from about 1 to about 40, R 3  is H, lower (C 1  -C 4 ) alkyl or an acetate. This polymer may also be used in concert with topping agents such as phosphoric acids, phosphonic acids, amines, metal chelating agents and oxygen scavengers.

FIELD OF THE INVENTION

The present invention pertains to a method of utilizing novel polymersto control the formation and deposition of scale imparting compounds insteam generating systems such as boiler water systems.

BACKGROUND OF THE INVENTION

As detailed in the Betz Handbook of Industrial Water Conditioning, 8thEdition, 1980, Betz Laboratories, Inc., Trevose, Pa., Pages 85-96, theformation of scale and sludge deposits on boiler heating surfaces is aserious problem encountered in steam generation. Although currentindustrial steam producing systems make use of sophisticated externaltreatments of the boiler feedwater, e.g., coagulation, filtration,softening of water prior to its feed into the boiler system, theseoperations are only moderately effective. In all cases, externaltreatment does not in itself provide adequate treatment since muds,sludge, silts and hardness-imparting ions escape the treatment, andeventually are introduced into the steam generating system.

In addition to the problems caused by mud, sludge or silts, the industryhas also had to contend with boiler scale. Although external treatmentis utilized specifically in an attempt to remove calcium and magnesiumfrom the feedwater, there is always a potential for scale formation dueto residual hardness, i.e., calcium and magnesium salts. Accordingly,internal treatment, i.e., treatment of the water fed to the system, isnecessary to prevent, reduce and/or retard formation of the scaleimparting compounds and their resultant deposition. The carbonates ofmagnesium and calcium are not the only problem compounds as regardsscale, but also water having high contents of phosphate, sulfate andsilicate ions either occurring naturally or added for other purposescause problems since calcium and magnesium and any iron or copperpresent, react with each and deposit as boiler scale. As is obvious, thedeposition of scale on the structural parts of a steam generating systemcauses poorer circulation and lower heat transfer capacity, resultingaccordingly in an overall loss of efficiency.

SUMMARY OF THE INVENTION

It has been discovered that certain water soluble copolymers, as shownin Formula I hereinafter, are effective in controlling the formation ofmineral deposits and in transporting and removing hardness found insteam generating systems such as boiler water systems.

The water soluble copolymers of the invention have the structure:##STR3## wherein E is the repeat unit remaining after polymerization ofan alpha, beta ethylenically unsaturated compound, R₁ is H or lower (C₁-C₄) alkyl, ##STR4## or a mixture of both, and n is an integer of fromabout 1 to about 40, R₃ is hydrogen, lower (C₁ -C₄) alkyl, or an acetateformed as a cap on the polyethyleneglycol methacrylate by reacting anacetylating agent with polyethyleneglycol methacrylate to produce anacetate capped polyethyleneglycol methacrylate which is then reactedwith the alpha, beta ethylenically unsaturated compound E to form thecopolymer of Formula I, c is the molar percentage being between 0-95molar %, d is the molar percentage being between 100-5 molar %, c and dshould add up to 100%.

RELATED ART

U.S. Pat. Nos. 4,326,980 and 4,828,713 disclose the utility of using apolymeric dispersant with a surfactant like molecule in steam generatingapplications. The combination of these two species provides increaseddeposit control activities in chelant/polymer and polymer/phosphateprograms. However, experimental data showed that in a coordinatedphosphate/pH program or an all polymer program, there was no superiorperformance benefit from a polymer plus surfactant approach.

U.S. Pat. No. 4,457,847 to Lorenc et al discloses a method of treatinghardness in boiler waters by using a water-soluble anionic vinyl polymercontaining at least 30 weight percent of carboxylate functionality andwith a chelation value of at least 200. The present invention differsfrom the '847 patent by using a novel copolymer containing a newcomonomer, polyethyleneglycol (meth)acrylate, low carboxylate contentand with a chelation value less than 200. None of these traits issuggested in the '847 patent.

Chemical Abstracts 111:200688c, 97:133338r, 111:59631v, 109:96974p and109:133509p teach using acrylic acid/polyethyleneglycol monomethacrylatecopolymers for concrete, reverse osmosis and cooling scale inhibitionapplications.

Chemical Abstract 99:736026 discloses injecting polyethyleneglycolmethacrylate, ammonium persulfate solution and triethanolamine intopetroleum wells to prevent fire.

The monomer, polyethyleneglycol methacrylate, has been used in emulsionpolymerization to improve the mechanical and freeze thaw stabilities oflatex particles.

The use of the copolymers of this invention for boiler water treatmentis not disclosed in the prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the invention, it has been discovered that certainwater soluble copolymers, as shown in Formula I hereinafter, areeffective in controlling the formation of mineral deposits and intransporting and removing hardness ions found in steam generatingsystems such as boiler water systems.

The water soluble copolymers of the invention have the structure:##STR5## where E of Formula I comprises the repeat unit obtained afterpolymerization of an alpha, beta ethylenically unsaturated monomer,preferably a carboxylic acid, amide form thereof, or lower alkyl (C₁-C₆) ester or hydroxylated lower alkyl (C₁ -C₅) ester of such carboxylicacids. Exemplary compounds encompassed by E included, but are notrestricted to, the repeat unit formed by polymerization of acrylic acid,methacrylic acid, acrylamide, maleic acid or anhydride, fumaric acid,itaconic acid, 2-hydroxypropyl acrylate, styrene sulfonic acid, and2-acrylamido-2methylpropanesulfonic acid and the like. Water solublesalt forms of these acids are also within the purview of the invention.

R₁ in Formula I is H or lower (C₁ -C₄) alkyl, R₂ is (CH₂ --CH₂ --O)_(n),##STR6## or mixture of both, n is an integer of from about 1 to about40, R₃ is hydrogen, lower (C₁ -C₄) alkyl, or an acetate formed as a capon the polyethyleneglycol moiety by reacting an acetylating agent with a(meth)acrylate of polyethyleneglycol to produce an acetate cappedpolyethyleneglycol (meth)acrylate which is then reacted with the alpha,beta ethylenically unsaturated compound E to form the copolymer ofFormula I. Suitable acetylating agents include acetic acid, aceticanhydride, acetyl chloride, and the like as described in U.S. Pat. Nos.4,959,156 and 4,847,410 fully incorporated herein by reference. c is themolar percentage being between 0-95 molar %, d is the molar percentagebeing between 100-5 molar %, c and d should add up to 100%.

A preferred copolymer of the present invention includes acrylic acid,methacrylic acid or maleic acid/polyethyleneglycol monomethacrylatecopolymers of the general formula: ##STR7## wherein R₁ is H or lower (C₁-C₄) alkyl, R₂ is (CH₂ --CH₂ --O)_(n), ##STR8## or mixture of both, n isan integer of from 1 to about 40, R₃ is H, lower (C₁ -C₄) alkyl or anacetate, R₄ is H or COOM, R₅ is H or (C₁ -C₄) alkyl and M is H or awater soluble cation, c is the molar percentage being between 0-95 molar%, d is the molar percentage being between 100-5 molar %, c and d shouldadd up to 100%. Acrylic acid (R₄ =H, R₅ =H) or methacrylic acid (R₄ =H,R₅ =CH₃) may be replaced with maleic acid (R₄ =COOH, R₅ =H) in FormulaII.

A homopolymer of polyethyleneglycol monomethacrylate is within the scopeof the present invention.

The number average molecular weight of the water soluble or waterdispersible copolymers of Formulas I or II is not critical and may fallwithin the Mn range of about 1,000 to 100,000 desirably, 1,000 to 30,000and more desirably 1,500 to 10,000. The key criteria is that thecopolymer be water soluble or water dispersible. Water soluble or waterdispersible terpolymers comprising monomer c and d of Formula I may alsobe effective for use in the present invention. Also, minor amounts ofadditional monomers may be added to the polymers.

Polyethyleneglycol monomethacrylate (HEM) is prepared by ethoxylation ofmethacrylate esters. These compounds are commercially available fromRhone-Poulenc under the SIPOMER® Trademark. The monomers are thencopolymers with methacrylic acid or maleic acid to obtain the copolymersof the invention. Polyethyleneglycol monomethacrylate may also bepolymerized to form a homopolymer. The polymerization may proceed inaccordance with conventional solution, precipitation or emulsionpolymerization techniques. Conventional polymermization initiators suchas azo compounds, persulfates, peroxides, UV light, etc., may be used.Chain transfer agents such as alcohols (preferably isopropanol), amineor mercapto compounds may be used to regulate the molecular weight ofthe polymer. The resulting polymer may be isolated by well knowntechniques including precipitation, etc. If polymerized in water, thepolymer may simply be used in its aqueous solution.

The polymers should be added to the boiler aqueous system, for whichcorrosion inhibiting, and/or deposit control activity is desired, in anamount effective for the purpose. This amount will vary depending uponthe particular system for which treatment is desired and will beinfluenced by factors such as, the area subject to corrosion, pH,temperature, water quantity and the respective concentrations in thewater of the potential scale and deposit forming species. For the mostpart, the polymers will be effective when used at levels of about0.1-500 parts per million parts of water. The polymers may be addeddirectly into the desired water system in a fixed quantity and in thestate of an aqueous solution, continuously or intermittently.

The polymers of the present invention provide superior deposit controlin several boiler treatment programs including coordinated in severalboiler treatment programs including coordinated phosphate/pH,chelant/polymer, and notably, all polymer programs. The polymers alsoincrease iron and hardness transport in the all polymer program.

In addition to superior deposit control performance, these polymersprovide several application advantages that make them superior additivesfor steam generating systems. The advantages circumvent problems withformulation difficulties, increased boiler solids, and feedwater traincorrosion problems. A description of each of these additional advantagesis as follows.

First, although proven viable, the conventional polymer plus surfactanttreatment as disclosed in U.S. Pat. No. 4,828,713 has problems with theformulation of concentrated solutions. The high concentrations ofpolymer and surfactant needed for product storage are also not possible.In contrast the new polymers provide a single water soluble component.In addition, neutralized acrylate and methacrylate polymers presentformulatory problems when adding phosphate salts to the final product.The new polymers eliminate, or greatly reduce this problem.

Second, a current all polymer program using poly sodium (meth)acrylateas disclosed in U.S. Pat. No. 4,457,847 contains notable concentrationsof neutralizing inorganics that can result in increased total boilersolids, affect pH control in high purity systems, and affectconductivity monitoring in the blowdown. There have been severalattempts to produce polymers neutralized with amines, but formulatoryand expense problems made this impossible. The polymers of the inventioneliminate or greatly reduce any additional neutralizing inorganics thatcan cause increased dissolved solids. They provide the first true allpolymer additive and signficantly reduce the deleterious effects ofadditional salts.

Third, it has been shown that compounds having a large lower temperaturechelating strength have the potential for corroding feedwater trainsprior to reaching the operating pressures of boilers (NACE 1991, paper#218). Most chelants and commercial anionic polymers have chelationvalues (the milligrams of hardness sequestered per gram of sequestrantor active polymer) greater than 200 ) U.S. Pat. No. 4,457,847).

These same high chelation value compounds are suspected of havingcorrosion potential in feedwater heaters where the buffering strength isweak compared to cycled steam generating conditions. Under feedwaterconditions the higher chelating species has the opportunity to sequestermetals from the metallurgy of the feedwater train. The polymers of theinvention have chelation values substantially lower than those anionicpolymers cited in U.S. Pat. No. 4,456,847 and have minimal potential forfeedwater train corrosion.

The use of the polymers disclosed herein is not limited to steamgenerating or boiler systems, exclusively. For instance, they may besuccessively utilized in cooling water systems, gas scrubbing systemsand the like where the formation and deposition of scale forming speciesis a problem.

The water soluble polymers of the present invention can also be usedwith topping agent components in order to enhance the corrosioninhibition and scale controlling properties thereof. For instance thepolymers may be used in combination with one or more kinds of compoundsselected from the group consisting of phosphoric acids and phosphonicacids and water soluble salts thereof, oxygen scavengers and metalchelating agents. Such topping agents may be added to the system in anamount of from about 1 to 500 ppm. The weight ratio of the polymer totopping agents may vary from 100:1 to 1:5.

Examples of such phosphoric acids include condensed phosphoric acids andwater soluble salts thereof. The phosphoric acids include anorthophosphoric acid, a primary phosphoric acid and a secondaryphosphoric acid. Condensed phosphoric acids include polyphosphoric acidssuch as pyrophosphoric acid, tripolyphosphoric acid and the like,metaphosphoric acids such as trimetaphosphoric acid, andtetrametaphosphoric acid.

As to the phosphoric acid derivatives which are to be added in additionto the polymers of the present invention, there may be mentionedaminopolyphosphonic acids such as aminitrimethylene phosphonic acid,ethylenediaminetetramethylene phosphonic acid and the like, methylenediphosphonic acid, hydroxyethylidene diphosphonic acid,2-phosphonobutane 1,2,4-tricarboxylic acid, etc. The polymers may beused in combination with yet other topping agents including corrosioninhibitors for iron, steel, copper, copper alloys or other metals,conventional scale and contamination inhibitors, metal chelating agentsand other conventional water treatment agents. Other corrosioninhibitors comprise tungstate, nitrites, borates, silicates,oxycarboxylic acids, catechols, and aliphatic amino surface activeagents. Other scale and contamination inhibitors include ligninderivatives, tannic acids, starch, polyacrylic soda, polyacrylic amide,etc. Metal chelating agents include polymaines, such as ethylenediamine,diethylenetriamine and the like and polyaminocarboxylic acids, such asnitrilotriacetic (NTA), ethylene diaminetetraacetic acid (EDTA),diethylenetriamine pentaacetic acid,hydroxyethylethylenediaminetriacetic acid (HEDTA), and salt forms of theacids mentioned.

The present polymers can also be used along with chemicals that arecapable of reducing dissolved oxygen in boiler water systems. Thechemicals refereed to as oxygen scavengers, comprise: hydrazine,sulfite, bisulfite, hydroquinone, carbohydrazide, alkyl hydroxylamines,and alkylamine, citric acid, ascorbic acid and its analogs or saltforms, etc. Amines such as morpholine, cyclohexylamine, piperazine,ammonia, various alkylhydroxylamines such as diethylaminoethanol,dimethylisopropanolamine, and diethylhydroxylamine, etc. may be usedwith the polymers of the invention in steam generating systems.

The water soluble polymers may be added separately to the aqueous systemor may be blended with the above topping agents compounds and then addedin the state of aqueous solution into the water system eithercontinuously or intermittently.

EXAMPLES

The invention will be further described with reference to a number ofspecific examples which are to be regarded solely as illustrative, andnot as restricting the scope of the invention.

EXAMPLE 1 Preparation of Methacrylic Acid/PolyethyleneglycolMonomethacrylate(HEM-10) Copolymer Molar Ratio 7.2/1

A suitable flask was equipped with a condenser, addition funnel,mechanical stirrer, thermometer and a nitrogen sparger. A mixed monomersolution containing 47.64 g of methacrylic acid (0.554 mol) and 48.7 gof HEM-10 (0.0768 mol, 83%) was placed in the addition funnel. 130.0 gof deionized water and 8.0 g of sodium persulfate were charged to theflask. This solution was sparged with nitrogen for 20 minutes thenheated to 85° C. maintaining the nitrogen sparge. The mixed monomersolution was then added to the flask over a period of 75 minutes. Onehour after this addition was complete an additional 3 cc of a 9%persulfate solution was added to the reaction mixture. The resultingmixture was heated for two more hours at 85° C. then cooled to roomtemperature. Caustic (50%) was then added to the solution to adjust thepH to 5.5.

The polymer solution, after being diluted to 30% solids had a Brookfieldviscosity of 261 cps at 25° C. The structure of the copolymer wasverified by 13C NMR. The spectrum was characterized by a broad poly(methacrylic acid)-type backbone, strong resonances at 60, 69 and 71 ppmcorresponding to the polyethyleneglycol moiety and a broad carbonylregion (177-183 ppm). There was no sign of residual monomer.

EXAMPLES 2-7

Similar procedures were used to prepare various copolymers ofmethacrylic acid/polyethyleneglycol monomethacrylate with different moleratios and degree of ethoxylation, n. The results are shown in Table I.

EXAMPLE 8 Homopolymer of Polyethyleneglycol Monomethacrylate (HEM-5)

Utilizing the apparatus as described in Example 1, 30.0 g of deionizedwater, 30.0 g of isopropanol and 2.2 g of sodium persulfate were chargedto the flask. 60.0 g of HEM-5 and 12.0 g of a 16.6% sodium persulfatesolution were added to the reaction mixture over 150 minutes (80C). Thereaction product was heated for one more hour followed by azeotropicremoval of isopropanol/water. The reaction mixture was then cooled toroom temperature and adjusted to the proper pH with 50% sodiumhydroxide.

The homopolymer, after being diluted to 30% solids has a Brookfieldviscosity of 40.9 cps at 25° C. The polymer was characterized by 13C NMRwhich showed the broad polymethacrylate type backbone, sharp resonancesat 60, 69 and 70 ppm from the polyethylene glycol moiety and broad butwell defined carbonyl resonances at 178 and 179 ppm. There was no signof residual monomer.

EXAMPLE 9 Homopolymer of Polyethyleneglycol Monomethacrylate (HEM-10)

Utilizing the apparatus and procedure as described in Example 8,homopolymer of HEM-10 was prepared. The homopolymer, after being dilutedto 30% solids has a Brookfield viscosity of 36.8 cps at 25° C. Thestructure of the homopolymer was confirmed by C13 NMR.

Table 1 summarizes the structure and physical properties of the polymersemployed in the examples.

Commercial polymers A, B and C are used as standards for comparison. Themolecular weight is obtained by a standard GPC analysis.

                  TABLE I                                                         ______________________________________                                                                           Brook-                                                                              Mol.                                                                    field Wt.                                         Polymer     Copolymer %     Visc. (GPC)                                Polymer                                                                              Composition Ratio     Solids                                                                              (cp.) Mn                                   ______________________________________                                        1      MAA/HEM 10  7.2/1     31.0  179   4300                                 2      MAA/HEM 10  3.6/1     30.1  261   5800                                 3      MAA/HEM 5     6/1     29.9  153   4000                                 4      MAA/HEM 10  2.4/1     30.4  127.5 6000                                 5      MAA/HEM 10  2.4/1     29.8  255.5 5900                                 6      MAA/HEM 10  2.4/1     29.6   48.8 4900                                 7      MAA/HEM 10  2.4/1     30.1   79.1 4700                                 8      HEM 5                 32.2   40.9 2700                                 9      HEM 10                30.3   36.8 4600                                 A      PMAA                  30.0        8000                                 B      AA/AM       2.4/1     26.4                                             C      PAA                   50.0        3000                                 ______________________________________                                         MAA = methacrylic acid                                                        PMAA = polymethacrylic acid, sodium salt                                      PAA = polyacrylic acid, sodium salt                                           HEM 10 = Polyethyleneglycol monomethacrylate, having an average of 10         moles of ethylene oxide                                                       HEM 5 = Polyethyleneglycol monomethacrylate, having an average of 5 moles     of ethylene oxide                                                             AA/AM = commercial acrylic acid/acrylamide copolymer                          All GPC results are based on polyacrylic acid standards                       HEM 5 & 10 are sold by RhonePoulene under the tradename Sipomer          

CHELATION VALUES

Chelation values obtained in this invention are used as a tool tomeasure a polymer's ability to sequester ions at lower temperatures.These measurements are determined by bench top analysis. The method issimilar to that disclosed in U.S. Pat. No. 4,457,847.

The system for determining chelation values consisted of the followingequipment:

1) An Orion model 701A digital pH/mV meter with an Orion model 93-20Ca(2+) ion specific electrode and a Ag/AgCl reference electrode.

2) A Markson model 41064 pH meter (battery operated to avoid groundloops) using a Markson pH electrode model 13-620-108.

A calcium calibration curve is established each day. It is prepared withstandard solutions of 1, 10, 100, and 1000 ppm Ca(as CaCO₃). Theelectrode potentials (mV) is plotted vs log [Ca] as CaCO₃. Only the 10,100, and 1000 ppm potentials are used for the plot because the lowerconcentration shows notable deviation from linearity.

The test consists of titrating increments of a known concentration ofsequestrant into a known concentration of Ca (as CaCO₃) and plotting themg Ca (as CaCO₃) sequestered vs the grams of active sequestrant. Theinitial slope of the best fitting line which goes through the origin isthe chelation value.

Solutions of sequestrant are made using 0.5 grams of active sequestrantper 250 mls. All solutions are pared so as to maintain constant ionicstrength and pH through the tests; including the standards and titratingsolutions. Ionic strength is fixed using 1 ml of 4M KCL per 50 mls ofsolution. The pH of the sequestrant titrating solutions is brought to10.0 with 1.0M KOH. During the calibration and titration, the pH wasmaintained at 10 with 0.1M KOH. A 100 ppm Ca (as CaCO₃) standardsolution is used as the test solution for all titrations.

By this methodology, calcium chelation values for the new polymers ofthis invention were measured. Table II lists these results along withseveral current boiler treatment polymers as cited in U.S. Pat. No.4,457,847. The values in this test are substantially lower than theprescribed minimum for acceptable boiler treatment chemicals. The newboiler treatment polymers do not have chelation values above the 200threshold level, and many are substantially below this.

                  TABLE II                                                        ______________________________________                                        Calcium Chelation Values                                                      Compound     Chelation Value                                                  ______________________________________                                        EDTA         328                                                              Polymer A    356                                                              Polymer B    306                                                              Polymer C    351                                                              Example 1    191                                                              Example 2    137                                                              Example 3    166                                                              Example 4     98                                                              Example 5     57                                                              Example 6     83                                                              Example 7     92                                                              Example 8    <10                                                              Example 9    <10                                                              ______________________________________                                         EDTA = Ethylenediaminetetraacetic acid                                   

The chelation value does not change substantially after the polymer isheat treated at typical boiler pressures of 600 psig for up to 6 hours(Table III). A 2 hour residence time exceeds the residence time in afeedwater train but does not approach the residence time of a typicaldrum boiler. The 6 hour residence time approaches that of the ResearchBoiler used in this test. The chelation value of the new polymer remainslow at these two extreme conditions, an indication that the polymer hasnegligible corrosive tendencies in a boiler or boiler feedwater system.

                  TABLE III                                                       ______________________________________                                        Calcium Chelation Values of Polymer 8                                         (Heat Treated at 600 psig in 10 ppm Phosphate)                                Time        Chelation Value                                                   ______________________________________                                        0 Hrs       <10                                                               2 Hrs       23                                                                6 Hrs       26                                                                ______________________________________                                    

The characteristics described above show how these polymers of thepresent invention are novel and a substantial improvement over currentlyused boiler polymers. The following boiler studies further provideevidence of how these polymers provide superior performance in both alow to medium pressure all polymer chelant program, a chelant/polymerprogram and a medium to high pressure coordinated PO₄ /pH program.

BOILER STUDIES

In order to assess the efficacy of the polymers of the present inventionin inhibiting scale formation in steam generating systems, researchboilers were fitted with two 4,000 watt electrical heater probes, giving185,000 BTU/ft² / hr and about 8 Kg/hr steam. The boiler feedwatercontained the containments and treatment agents given herein below. Theboilers were operated for 44 hours per run at an average of 15 cycles ofconcentration. At the conclusion of each run, the deposits were cleanedfrom the probes with an acid solution and the deposit densities werethen calculated based on the known probe surface areas.

During the 44 hour runs, daily blowdown (BD) samples are submitted forcalcium, magnesium, and/or iron analysis. The average of daily analysisare used to monitor transport of each contaminate (in ppm) out of theboiler.

                  TABLE IV                                                        ______________________________________                                        Polymer Performance in an "All Polymer" Program                               Conditions:  600 psig                                                                      4:1:1 Ca:Mg:Fe (ppm)                                                          Polymer actives/hardness 1/1                                                  hydroquinone as oxygen scavenger                                            Ave.     BD Ca     BD Mg  BD Fe                                               Deposit  (Ave.     (Ave.  (Ave.                                    Polymer    g/ft.sup.2                                                                             ppm)      ppm)   ppm)                                     ______________________________________                                        Example 1* 0.193    24.3      1.4    0.6                                      Example 2* 0.217    26.0      3.3    2.1                                      Example 3* 0.285    30.6      5.8    2.2                                      Example 4  0.251    24.5      1.3    0.33                                     Example 5  0.204    27.7      3.3    2.4                                      Example 6  0.221    30.3      8.1    3.6                                      Example 7  0.196    21.8      0.8    0.4                                      Example 8  0.181    15.8      2.5    1.8                                      Example 8  0.124    20.4      7.8    3.7                                      Example 9  0.179    13.5      1.2    0.9                                      Example 9  0.081    10.3      3.3    3.1                                      Polymer A  0.297    28.2      4.3    1.4                                      Polymer B  2.824    5.0       1.6    0.6                                      Polymer C  4.245    4.8       1.7    0.3                                      Blank      1.166    2.8       0.8    0.1                                      ______________________________________                                         BD = boiler blowdown                                                          *addition of antifoam UCON ® 5100                                    

Table IV shows the effectiveness of these polymers and copolymers inreducing deposition on the heat transfer surfaces of the ResearchBoilers in an all polymers treatment program. The blank run in thistable shows substantial deposition of calcium, magnesium and iron on thesurfaces. In addition to heavy deposition, the blank run shows noevidence of transport of contaminates by boiler blowdown. The blowdownnumbers are notably lower than any of the systems with a treatmentadditive and indicate a need for a boiler treatment program.

Comparative polymers B and C show higher deposit weights than the blank.This increase is due to calcium deposition.

The polymers of the invention listed in Table IV show better performancethan the commercial polymers currently used for boiler treatment. Thelower deposits are reflected by a notable increase in the transport ofthe contaminates.

                  TABLE V                                                         ______________________________________                                        Polymer Performance in a Coordinated PO.sub.4 /pH Program                     Conditions:    1450 psig                                                                     2.5 ppm Fe feed                                                               20 ppm Ortho -PO.sub.4                                                        pH 9.75-10.00                                                                 Hydrazine as oxygen scavenger                                               Ave.                                                                          Deposit  BD Fe       BD Fe                                       Treatment    (g/ft.sup.2)                                                                           (ppm, Day 1)                                                                              (ppm, Day 2)                                ______________________________________                                        Blank        2.109    0.47        0.19                                                     2.377    0.71        1.16                                        10 ppm Polymer A                                                                           0.963    0.50        0.16                                                     0.638    0.11                                                    20 ppm Polymer A                                                                           0.729    0.24        0.50                                                     0.599    0.09        0.28                                        10 ppm Example 6                                                                           0.462    1.38        0.95                                        10 ppm Example 7                                                                           0.511    0.30        0.51                                        10 ppm Example 8                                                                           0.286    0.48        0.48                                        10 ppm Example 9                                                                           0.567    0.50        0.39                                        ______________________________________                                         Polymer A: polymethacrylic acid, sodium salt                             

Table V lists results for the evaluation of these polymers in acoordinated PO₄ /pH program with high iron contaminate concentration.This test methodology is typical of a higher pressure boiler system witha demineralized pretreatment program, and is very different from theprevious test system. Test polymers were fed as 10 ppm PMAA, where theconcentration fed was determined using the ratio of equivalent weightsof PMAA to the test polymer.

The results in Table V show that these new polymers are superior topolymethacrylic acid and a commonly used polymer for boiler watertreatment.

                  TABLE VI                                                        ______________________________________                                        Polymer Performance in a Chelant/Polymer Research Boiler                      Program                                                                              600 p.s.i.g.                                                                  4:1:1 Ca:Mg:Fe (ppm)                                                          Chelant fed at 0.5:1 stoichiometry                                            Hydroquinone as oxygen scavenger                                               Ave. Deposit                                                                             BD Fe     BD Ca   BD Mg                                    Treatment                                                                             (g/ft.sup.2)                                                                             (ppm Ave.)                                                                              (ppm, ave.)                                                                           (ppm, ave.)                              ______________________________________                                        Blank   2.873      0.07       8.40   0.81                                     Polymer A                                                                             0.270      3.95      23.60   6.65                                     Example 4                                                                             0.196      0.10      18.15   1.06                                     ______________________________________                                         Chelant: EDTA                                                            

The results listed in Table VI show the performance of the Example 3polymer of the invention as compared to polymethacrylic acid in thechelant/polymer program.

The Research Boiler data shows that the polymers of the invention areeffective at reducing deposition and increasing transport hardness inthree substantially different boiler programs. In addition, thesepolymers show no potential of being corrosive in the feedwater train asindicated by their chelation values and are a substantial improvementover the deleterious effects encountered with currently practicedtechnology. In addition to the effectiveness of these polymers in boilertreatment programs, the polymers contain much lower concentrations ofsodium, thus resulting in less dissolved solids in the boiler. All thesetraits make the polymers of the invention a novel contribution to boilerwater treatment.

What we claim is:
 1. A method of controlling the deposition of scaleimparting precipitates including calcium, magnesium and iron on thestructural parts of a system exposed to an aqueous medium containingscale imparting precipitates under steam generating conditionscomprising adding to the aqueous medium an effective amount for thepurpose of a water soluble polymer having the structure ##STR9## whereinR₁ is H or lower (C₁ -C₄) alkyl, R₂ is (CH₂ --CH₂ --O)_(n), ##STR10## ora mixture of both, and n is an integer of from about 1 to about 40, R₃is H, lower (C₁ -C₄) alkyl or an acetate, R₄ is H or COOM, R₅ is H orlower (C₁ -C₄) alkyl and M is H or a water soluble cation; and, whereinc is from 0-95 molar percent and d is from 100-5 molar percent, with theproviso that c and d add up to 100 percent and the water soluble polymerhas a calcium chelation value below
 200. 2. The method of claim 1wherein the polymer has a molecular weight (Mn) of between about 1,000and 100,000.
 3. The method of claim 2 wherein the polymer has amolecular weight (Mn) of between about 1,000 and 30,000.
 4. The methodof claim 3 wherein the polymer has a molecular weight (Mn) of betweenabout 1,500 and 10,000.
 5. The method of claim 1 wherein water solublepolymer is added to the aqueous medium in an amount of 0.1-500 partspolymer based upon 1 million parts of the aqueous medium.
 6. The methodof claim 1 further comprising adding to the aqueous medium an effectiveamount for the purpose of a topping agent selected from the groupconsisting of phosphoric acids and water soluble salts thereof,phosphonic acids and water soluble salts thereof, amines and metalchelating agents.
 7. The method of claim 6 wherein the phosphoric acidis a member selected from the group consisting of orthophosphoric acid,pyrophosphoric acid, tripolyphosphoric acid, trimetaphosphoric acid,tetrametaphosphoric acid and water soluble salts thereof.
 8. The methodof claim 6 wherein the phosphonic acid is a member selected from thegroup consisting of ethylene diaminetetramethylene phosphonic acid,methylene diphosphonic acid, hydroxyethylidene diphosphonic acid and2-phosphonobutane 1,2,4-tricarboxylic acid.
 9. The method of claim 6wherein the amine is a member selected from the group consisting ofmorpholine, cyclohexylamine, piperazine, ammonia, diethylaminoethanol,dimethylisopropanolamine and diethylhydroxylamine.
 10. The method ofclaim 1 further comprising adding to the aqueous medium an oxygenscavenger.
 11. The method of claim 10 wherein the oxygen scavenger isselected from the group consisting of hydrazine, sulfite, bisulfite,hydroquinone, carbohydrazide, alkylhydroxylamines, and alkylamine,citric acid, ascorbic acid and its analogs or salt forms thereof. 12.The method of claim 6 wherein the metal chelating agent is selected fromthe group consisting of ethylenediamine, diethylenetriamine, nitrilotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, hydroxyethylethylenediaminetetraacetic acid and watersoluble salts thereof.
 13. The method of claim 6 wherein the toppingagent is added to said system in an amount of 1 to about 500 parts permillion parts of the aqueous medium.
 14. The method of claim 1 whereinthe system is a boiler system.
 15. The method of claim 1 wherein R₄ isH, R₅ is CH₃ an M is H or a water soluble cation.
 16. A method oftransporting and removing hardness including calcium, magnesium and ironfound in an aqueous medium under steam generating conditions comprisingadding to the aqueous medium an effective amount for the purpose of awater soluble polymer having the structure ##STR11## wherein R₁ is H orlower (C₁ -C₄) alkyl, R₂ is (CH₂ --CH₂ --O)_(n), ##STR12## or a mixtureof both, n is an integer of from about 1 to about 40, R₃ is H, lower (C₁-C₄) alkyl or an acetate, R₄ is H or COOM, R₅ is H or lower (C₁ -C₄)alkyl and M is H or a water soluble cation; and, wherein c is from 0-95molar percent and d is from 100-5 molar percent, with the proviso that cand d add up to 100 percent and the water soluble polymer has a calciumchelation value below
 200. 17. The method of claim 16 wherein thepolymer has a molecular weight (Mn) of between about 1,000 and 100,000.18. The method of claim 17 wherein the polymer has a molecular weight(Mn) of between about 1,000 and 30,000.
 19. The method of claim 18wherein the polymer has a molecular weight (Mn) of between about 1,000and 10,000.
 20. The method of claim 16 wherein water soluble polymer isadded to the aqueous medium in an amount of 0.1-500 parts polymer basedupon 1 million parts of the aqueous medium.
 21. The method of claim 16further comprising adding to the aqueous medium an effective amount forthe purpose of a topping agent selected from the group consisting ofphosphoric acids and water soluble salts thereof, phosphonic acids andwater soluble salts thereof, amines and metal chelating agents.
 22. Themethod of claim 21 wherein the phosphoric acid is a member selected fromthe group consisting of orthophosphoric acid, primary phosphoric acid,secondary phosphoric acid, pyrophosphoric acid, tripolyphosphoric acid,trimetaphosphoric acid, tetrametaphosphoric acid and water soluble saltsthereof.
 23. The method of claim 21 wherein the phosphonic acid is amember selected from the group consisting of aminotrimethylenephosphonic acid, ethylenediaminetetramethylene phosphonic acid,methylenediphosphonic acid, hydroxyethylidene diphosphonic acid and2-phosphonobutane 1,2,4-tri-carboxylic acid.
 24. The method of claim 21wherein the amine is a member selected from the group consisting ofmorpholine, cyclohexylamine, piperazine, ammonia, diethylaminoethanol,dimethylisopropanolamine, and diethylhydroxylamine.
 25. The method ofclaim 16 further comprising adding to the aqueous medium an oxygenscavenger.
 26. The method of claim 25 wherein the oxygen scavenger isselected from the group consisting of hydrazine, sulfite, bisulfite,hydroquinone, carbohydrazide, alkylhydroxylamines, and alkylamine,citric acid, ascorbic acid and its analogs or salt forms thereof. 27.The method of claim 21 wherein the metal chelating agent is selectedfrom the group consisting of ethylenediamine, diethylenetriamine,nitrilo triacetic acid, ethylenediaminetetraacetic acid,diethylenetriamine pentaacetic acid,hydroxyethylethylenediaminetetraacetic acid and water soluble saltsthereof.
 28. The method of claim 21 wherein the topping agent is addedto said system in an amount of 1 to about 500 parts per million parts ofthe aqueous medium.
 29. The method of claim 16 wherein the system is aboiler system.
 30. The method of claim 16 wherein R₄ is H, R₅ is CH₃ andM is H or a water soluble cation.